The invention relates to administering devices, including injection devices, and methods of their operation and use. More particularly, it relates to a reservoir module which has an associated piston rod, and a dispensing or administering apparatus comprising such a reservoir module.
In a preferred embodiment, the product dispensing or administering apparatus is an injection apparatus or inhalation apparatus for medical, therapeutic, diagnostic, pharmaceutical or cosmetic applications. One preferred example of injection apparatus is injection pens, in particular semi-disposable pens.
WO 97/17095 describes an injection apparatus consisting of a dosing and activating module and a reservoir module which are detachably connected to each other. The reservoir module is designed as a disposable module, while the dosing and activating module is intended to be re-used—once the reservoir module has been used up or emptied—with a new reservoir module. The reservoir module contains a reservoir for a product to be injected and mounts a piston rod which acts on a piston accommodated in the reservoir to deliver product. The piston rod comprises an outer thread which is in threaded engagement with an inner thread of a dosing setting member. The piston rod is linearly guided, such that when the dosing setting member is rotated, the piston rod is moved towards the piston and a slight distance between a front end of the piston rod and the piston is thus changed. The reservoir module also mounts the dosing setting member and thus comprises the piston rod and the dosing setting member, which are disposed of together with the reservoir as a single module, after the reservoir as been emptied.
An advantage of the design of such semi-disposable injection apparatus is that the parts of the injection apparatus involved in dosing and delivery only have to be configured for delivering the contents of a single reservoir. This reduces the price of these parts. Since, if repeatedly used, such parts would always have to be guided back again to an initial position by the user, they would furthermore be exposed to a risk of damage which should not be underestimated. The reliability of correctly selecting and delivering the dosage need not therefore be less for semi-disposable injection apparatus than for completely re-usable apparatus. Moreover, exchanging a complete reservoir module is simpler than exchanging only a reservoir.
The dosage setting member of the known apparatus is pushed into a rear position, in which the product is dosed, by a pressure spring which is supported by a casing of the reservoir module. By dosing the product, the piston rod is advanced towards the piston relative to the dosage setting member and the casing of the reservoir module. The product is delivered by means of a dosing and activating device which is mounted in a casing of the dosing and activating module and pushes against a rear abutting area of the dosage setting member. The dosing and activating device pushes the dosage setting member, and due to the threaded engagement also the piston rod together with it, in the advancing direction.